The invention described herein may be manufactured, used, imported, sold, and licensed by or for the Government of the United States of America without the payment to me of any royalty thereon.
The present invention relates generally to the field of microstrip antennas, and more particularly to compact cylindrical microstrip antennas.
Microstrip antennas are of lightweight, low profile, low cost and can have a cylindrical and conformal structure, replacing bulky antennas. Monopole antennas are also a low cost type of antenna, but as the monopole antenna""s frequency goes down to VHF and lower frequencies, its length becomes too large and cumbersome, making it inapplicable for a number of applications. The length of each microstrip patch is about half of a wavelength within the dielectric medium under the radiating patch. Similarly, the size of an efficient monopole is quarter wavelength. Thus, when the frequency in low, the antenna size becomes larger.
The disadvantage of excessive monopole antenna length cannot be overcome by simply reducing length to less than a quarter wavelength, because the monopole antenna quickly loses its efficiency. Up until now, it has not been possible to employ microstrip antennas without the disadvantages, limitations and shortcomings associated with antenna length and size. The present invention makes it possible to have electrically small cylindrical microstrip antennas at low frequencies with a monopole-type radiation pattern. With this invention, an omni-directional compact microstrip antenna is provided for both VHF and even lower frequencies.
An electrically small cylindrical microstrip antenna at low frequencies offers a number of advantages over prior art antennas. The compact cylindrical microstrip antenna of the present invention provides the same high efficiency as a quarter wavelength monopole and conventional microstrip antennas, with the key advantage over prior art antenna structures of a substantially shorter antenna length. In addition to the advantages of high efficiency and small size, the present invention provides omnidirectional azimutahl patterns useful in many military and commercial communication systems, without suffering from the size limitations of prior art antenna structures.
It is an object of the present invention to provide a cylindrical microstrip antenna structure.
Another object of the present invention is to provide an electrically small cylindrical microstrip antenna with a radiation pattern similar to a monopole having a reduced antenna length that operates at low frequencies such as UHF and VHF.
These and other objects are advantageously accomplished with the present invention by providing a compact cylindrical microstrip antenna comprising a microstrip substrate wrapped around a section of a cylindrical ground plane, with conductive patches disposed on the microstrip substrate. In one embodiment of the present invention, a reduced antenna length of at least 10% of the length of a conventional microstrip antenna has been achieved, resulting in small microstrip antennas at lower frequencies.